1. The Field of the Invention
The present invention relates generally to improved methods for manufacturing supported catalysts and catalysts made by such methods. Anchored nanocatalyst particles are at least partially maintained in a non-zero oxidation state to increase anchoring strength, catalyst particle stability, and particle dispersion during a heat treatment process.
2. The Relevant Technology
It is sometimes desirable to subject catalysts to a heat treatment process (sometimes referred to as “calcining”) in order to drive off solvents and unwanted organic compounds that may inhibit catalytic activity and/or to help coalesce metal catalyst atoms to form solid catalyst particles or crystals. This is particularly true of catalysts that are attached to a solid support using solvents or other materials that are not intended to remain with the catalyst during use. Supported and anchored reforming nanocatalysts are an example of a catalyst that works better when initially subjected to a heat treatment process (e.g., in terms of activity, selectivity, longevity and/or hydrogen production).
One problem associated with subjecting catalyst particles, including supported catalysts, to elevated temperature is the tendency of metal catalyst particles to become unstable, migrate and agglomerate together. Causing or allowing catalyst particles to agglomerate together decreases the overall surface area of the catalyst material and reduces catalyst distribution on the support surface. Because catalytic activity is proportional to both the surface area and distribution of the catalyst, excessive heat treatment can decrease catalytic activity, thus potentially offsetting the benefits derived by heat treatment.
Supported catalysts, in fact, often become spent or depleted as a result of harsh processing conditions, including high temperature, by the catalyst particles migrating and agglomerating together. Washing and burnoff to remove impurities only partially restores conventional catalysts to their original activity precisely because such processes cannot reverse the deleterious effects of catalyst particle migration and agglomeration.
Because many catalysts are made using expensive metals such as noble metals, there is a need to provide improved catalysts and methods that increase the activity and stability of such catalysts.